Despite the advent of many flight navigational aids, one of the most important tools for navigation of aircraft remains visual navigation. Many of today's aircrafts include various safety features such as on board radar, ground proximity warning systems, etc. that provide a pilot with added information about the airspace surrounding the aircraft. These systems are a tremendous resource to aid the pilot in obtaining better situational awareness during flight, by allowing the pilot to further interpret what the pilot is visually observing. However, there are instances where these various instruments become the pilot's only resource for information because the pilot's vision is hindered.
Visual hindrances may be due to bad weather, such as fog, snow, or rain, or they may be due to the time of day, such as night, dawn, or dusk. Further, some visual hindrances are due to the field of view limitations of the aircraft itself. Many aircraft cockpits have a field of view that is typically limited to a forward facing area that does not provide the pilot with adequate visualization to the sides and rear of the aircraft and also does not provide adequate vertical visualization above and below the aircraft.
Obstructed vision is an important safety concern in aircraft navigation, and there has been considerable effort devoted to providing systems that increase or enhance a pilot's view from the cockpit. Systems have been developed that include the use of one or more sensors that are located on the aircraft. The sensors are directed toward a selected field of view and provide images to a display system in the cockpit, where they are, in turn, displayed to the pilot. The sensors may be video cameras, infrared cameras, radar, etc. The systems allow the pilot to choose the types of images to view. For example, in nighttime flight or fog conditions, the pilot may opt to view images from the infrared and radar sensors, while under clear conditions, the pilot may use video camera feeds.
These systems may also include synthetic image sources. Specifically, many systems include mapping databases that include synthetic illustrations of various geographic features. These mapping databases can be coordinated with the actual position of the aircraft so that the synthetic images may be displayed to give the pilot a synthetic visualization of the terrain within the range of the aircraft.
An enhanced vision system (EVS) combines imagery from multiple sensors, providing an integrated awareness display to a user. An EVS may stitch imagery from sensors having different, perhaps partially overlapping fields of view (FOVs). An EVS may fuse imagery from different modality sensors (e.g., video, infrared or radar) having a common FOV. An EVS may combine sensor imagery with synthetic imagery, such as three dimensional terrain imagery from digital elevation maps, overhead satellite imagery, and/or flight path symbology. The output of an EVS is then typically displayed on a head-down, head-up, or helmet-mounted display (HMD).
One such EVS is disclosed in U.S. Pat. No. 5,317,394 to Hale et al., which is incorporated herein by reference. In this system, sensors are positioned on the exterior of the aircraft such that adjacent sensors have overlapped fields of view. Images from these various sensors are provided to a display system in the aircraft, where they are displayed to the pilot. The images are displayed in an overlapped configuration so as to provide a composite or mosaic image.
Other improvements to EVSs have been developed, such as those disclosed in U.S. Patent Application Publication No. 2004/0169617, entitled Systems and Methods for Providing Enhanced Vision Imaging with Decreased Latency, U.S. Patent Application Publication No. 2004/0169663, entitled Systems and Methods for Providing Enhanced Vision Imaging, and U.S. patent application Ser. No. 10/940,276, entitled Situational Awareness Components of an Enhanced Vision System, which are commonly assigned and incorporated herein by reference.
EVSs have been developed which include helmet-mounted display for displaying images from various sensors located on the aircraft. This type of system typically includes a helmet-tracking device that tracks movement of the pilot's head in order to determine the pilot's current line of sight (LOS) and field of view. Using this directional information, the system retrieves image data from the sensors that represent the line of sight in which the pilot is staring and displays this image on the helmet display. The image is updated as the pilot's head turns to different lines of sight.
In a conventional EVS in which the EVS display is located in proximity to the EVS processor, the EVS display, such as the HMD discussed above, is connected via a cable to the EVS. The cable may be, for example, an optical fiber cable. The EVS processor receives the user's LOS information via the cable from the HMD. The EVS processor then selects and blends the appropriate imagery to create an enhanced image. The enhanced image is sent via the cable to the HMD and displayed for the user. The cable connection between the EVS processor and the display enables full FOV, full frame rate, full resolution imagery to be sent and displayed continuously. Such a conventional EVS may be used, for example, in a manned aircraft.
Because of the multiple sensors of an EVS having different lines of sight and fields of view, EVSs are able to support multiple crew members of a single aircraft. For example, the view forward of the aircraft may be displayed for the pilot while the view below the aircraft may be displayed for the weapons operator.
The use of remotely-piloted or autonomously-piloted aircraft, often termed unmanned aerial vehicles (UAVs), is becoming more prevalent, particularly for military use. A UAV is typically controlled by a pilot located in a remote ground control station (GCS). The communication between the UAV and the GCS is via radio frequency (RF) or other wireless link, such as line-of-sight or Ku-band satellite communication.
In addition to the pilot, additional personnel, such as a weapons operator, may assist the pilot and may control aspects of the operation of the UAV. The additional personnel may be located in the same GCS as the pilot, or may be located in a separate GCS that may be located a great distance from the pilot's GCS.
In a conventional UAV, imagery from the UAV is sent to the GCS via the wireless link. The imagery may be provided by a gimbal-mounted camera system on the UAV. The direction in which the gimbal-mounted camera is directed (i.e., the camera's line of sight) may be controlled by the position of the pilot's HMD. This type of imagery system has drawbacks, however. The gimbal imposes drag and increases the radar signature of the UAV. Furthermore, when the camera is directed to view to the side or below the aircraft, as may be done for targeting purposes, there is no vision along the flight path of the UAV. Conversely, when the camera is directed along the flight path, as may be done for navigation purposes, there is no vision to the side or below the aircraft to enable the pilot to see and avoid potential threats to the UAV. This may be particularly problematic when the pilot requires a view along the flight path while a separate weapons operator requires a view below the UAV to target a weapon.
Because imagery from the UAV is transmitted to the GCS via the wireless link, issues may arise because of bandwidth limitations. The bandwidth of the wireless link between the UAV and the GCS may fluctuate for many reasons. Decreased bandwidth may prevent the GCS from receiving full field of view, full frame rate, full resolution imagery from the UAV. However, even when it is not possible to transmit full bandwidth imagery to the GCS, that imagery is available on board the vehicle and may be processed to provide warnings or other cueing to the remote human operators.
As such, there is a need for an imaging system for use with a UAV that will enable one or more remote users to receive imagery from different lines of sight without increased drag or radar signature. Additionally, there is a need for an imaging system that is capable of adjusting to fluctuations in the communication bandwidth while providing appropriate images to the users.